const std = @import("std");

const lua_version = "5.4.7";
const lua_short_version = "5.4";
const luarocks_version = "3.13.0";

pub fn build(b: *std.Build) void {
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});

    const panto_lib_dep = b.dependency("panto", .{
        .target = target,
        .optimize = optimize,
    });

    // The native Lua C-module (`libpanto-lua`). We embed its compiled
    // `panto.so` into the panto binary and stage it onto the embedded
    // VM's `package.cpath` at bootstrap, so `require('panto')` resolves
    // to the native agent/stream module on a cold, network-less machine
    // (the guaranteed initial module load — see
    // docs/step19-cli-panto-module-plan.md).
    const panto_lua_dep = b.dependency("panto_lua", .{
        .target = target,
        .optimize = optimize,
    });
    const panto_so_embed_path = generatePantoSoEmbed(b, panto_lua_dep);

    // TOML parser (used by the CLI for ~/.config/panto/models.toml).
    // We disable the upstream's optional thread-pool dep — we only need
    // sequential parsing of a small config file.
    const toml_dep = b.dependency("toml", .{
        .target = target,
        .optimize = optimize,
        .@"thread-pool" = false,
    });

    // Markdown parser for TUI rendering. MD4C is a small, permissively
    // licensed C CommonMark parser; Zig owns only terminal rendering.
    const md4c_dep = b.dependency("md4c", .{});

    // Fetch upstream Lua source (used both for our static library and
    // staged at runtime as the `include/` headers under the data home).
    // Reproducibility comes from the content-addressed hash in
    // build.zig.zon.
    const lua_src = b.dependency("lua_src", .{});
    const lua_anchor_path = generateLuaAnchor(b, lua_src);

    // Fetch luarocks source. We don't compile any of it — it's pure
    // Lua. The codegen step below produces a `embedded_luarocks.zig`
    // module that `@embedFile`s every script so the runtime can serve
    // them as `require("luarocks.*")` results without disk I/O.
    const luarocks_src = b.dependency("luarocks_src", .{});
    const luarocks_embed_path = generateLuarocksEmbed(b, luarocks_src);

    // Same trick for the Lua headers: bundle them so first-run
    // bootstrap can stage them under <data home>/rocks/lua-X.Y.Z/include/
    // for luarocks to find when compiling C rocks.
    const lua_headers_embed_path = generateLuaHeadersEmbed(b, lua_src);

    // And the in-repo `agent/` tree: bundled into the binary and
    // staged at <data home>/agent/ on first run. This is panto's
    // "base" extension/tool layer (read/write/edit/bash etc.).
    const agent_embed_path = generateAgentEmbed(b);

    // Constants module: makes Zig know the Lua and luarocks versions
    // without duplicating literals everywhere.
    const versions_mod = b.addOptions();
    versions_mod.addOption([]const u8, "panto_version", @import("build.zig.zon").version);
    versions_mod.addOption([]const u8, "lua_version", lua_version);
    versions_mod.addOption([]const u8, "lua_short_version", lua_short_version);
    versions_mod.addOption([]const u8, "luarocks_version", luarocks_version);
    // Absolute repo root, for tests that need to locate source-tree
    // assets (e.g. `agent/tools/*.lua`) regardless of the test
    // runner's cwd.
    versions_mod.addOption([]const u8, "repo_root", b.build_root.path orelse ".");

    // CLI executable
    const exe_mod = b.createModule(.{
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
        .link_libc = true,
    });
    exe_mod.addImport("panto", panto_lib_dep.module("panto"));
    exe_mod.addImport("toml", toml_dep.module("toml"));
    exe_mod.addImport("versions", versions_mod.createModule());
    exe_mod.addImport("embedded_luarocks", b.createModule(.{
        .root_source_file = luarocks_embed_path,
    }));
    exe_mod.addImport("embedded_lua_headers", b.createModule(.{
        .root_source_file = lua_headers_embed_path,
    }));
    exe_mod.addImport("embedded_agent", b.createModule(.{
        .root_source_file = agent_embed_path,
    }));
    exe_mod.addImport("embedded_panto_so", b.createModule(.{
        .root_source_file = panto_so_embed_path,
    }));
    // Link Lua. We can't use a static library here because the
    // standard archive-linking behavior drops object files whose
    // symbols nothing in our code references — e.g. `lua_settable`,
    // which luv.so needs at runtime via `dlopen` but neither panto
    // itself nor the embedded lua.c repl ever call directly. Instead,
    // compile the Lua sources directly *into* the executable's own
    // module so every object lands in the binary. `rdynamic = true`
    // below ensures the symbols are exported into the dynamic symbol
    // table for `dlopen`'d rocks to resolve.
    addLuaSources(exe_mod, lua_src, lua_anchor_path);
    exe_mod.addIncludePath(lua_src.path("src"));
    addMd4c(exe_mod, md4c_dep);

    // Compile lua.c (the upstream standalone interpreter, ~600 lines)
    // as a separate static library so we can route the `panto lua`
    // subcommand into its main() without it conflicting with our own
    // main().
    const lua_repl = buildLuaRepl(b, target, optimize, lua_src);
    exe_mod.linkLibrary(lua_repl);

    const exe = b.addExecutable(.{
        .name = "panto",
        .root_module = exe_mod,
    });
    // C rocks (luv.so and anything else loaded via dlopen) need
    // Lua's C API symbols to be findable in the running process's
    // symbol table. Without `-rdynamic`, the linker strips them as
    // unused-from-outside; `dlopen` then fails at load time with
    // "symbol not found in flat namespace '_lua_settable'" etc.
    exe.rdynamic = true;

    b.installArtifact(exe);

    const run_cmd = b.addRunArtifact(exe);
    run_cmd.step.dependOn(b.getInstallStep());
    if (b.args) |args| {
        run_cmd.addArgs(args);
    }

    const run_step = b.step("run", "Run the app");
    run_step.dependOn(&run_cmd.step);

    // CLI unit tests
    const test_mod = b.createModule(.{
        .root_source_file = b.path("src/main.zig"),
        .target = target,
        .optimize = optimize,
        .link_libc = true,
    });
    test_mod.addImport("panto", panto_lib_dep.module("panto"));
    test_mod.addImport("toml", toml_dep.module("toml"));
    test_mod.addImport("versions", versions_mod.createModule());
    test_mod.addImport("embedded_luarocks", b.createModule(.{
        .root_source_file = luarocks_embed_path,
    }));
    test_mod.addImport("embedded_lua_headers", b.createModule(.{
        .root_source_file = lua_headers_embed_path,
    }));
    test_mod.addImport("embedded_agent", b.createModule(.{
        .root_source_file = agent_embed_path,
    }));
    test_mod.addImport("embedded_panto_so", b.createModule(.{
        .root_source_file = panto_so_embed_path,
    }));
    addLuaSources(test_mod, lua_src, lua_anchor_path);
    test_mod.addIncludePath(lua_src.path("src"));
    addMd4c(test_mod, md4c_dep);
    test_mod.linkLibrary(lua_repl);

    const unit_tests = b.addTest(.{
        .name = "panto-tests",
        .root_module = test_mod,
    });

    const run_unit_tests = b.addRunArtifact(unit_tests);
    const test_step = b.step("test", "Run unit tests");
    test_step.dependOn(&run_unit_tests.step);

    // Also run libpanto's own tests as part of `zig build test`
    const lib_test_step = panto_lib_dep.builder.top_level_steps.get("test").?;
    test_step.dependOn(&lib_test_step.step);
}

fn addMd4c(mod: *std.Build.Module, md4c_dep: *std.Build.Dependency) void {
    const cflags = [_][]const u8{
        "-std=c99",
        "-Wall",
        "-Wextra",
        "-Wno-unused-parameter",
    };
    mod.addCSourceFile(.{
        .file = md4c_dep.path("src/md4c.c"),
        .flags = &cflags,
    });
    mod.addIncludePath(md4c_dep.path("src"));
}

/// Compile a thin wrapper around the upstream `lua.c` standalone
/// interpreter that exposes `pmain` for panto's `lua` subcommand to
/// invoke against a pre-configured `lua_State`.
///
/// We rename `main` to `lua_unused_main` so the symbol doesn't collide
/// with panto's `main` (the wrapper never references it; the linker
/// just needs a place for it to land).
fn buildLuaRepl(
    b: *std.Build,
    target: std.Build.ResolvedTarget,
    optimize: std.builtin.OptimizeMode,
    lua_src: *std.Build.Dependency,
) *std.Build.Step.Compile {
    const mod = b.createModule(.{
        .target = target,
        .optimize = optimize,
        .link_libc = true,
    });

    const cflags = [_][]const u8{
        "-std=gnu99",
        "-Wall",
        "-Wno-unused-parameter",
        "-Wno-unused-function",
        // Rename upstream `main` so it doesn't collide with panto's.
        // We never call it; the wrapper invokes `pmain` directly.
        "-Dmain=lua_unused_main",
    };

    mod.addCSourceFile(.{
        .file = b.path("build/panto_lua_repl.c"),
        .flags = &cflags,
    });
    // The wrapper `#include`s lua.c by name; we add lua_src/src to
    // the search path so `#include "lua.c"` resolves.
    mod.addIncludePath(lua_src.path("src"));
    addLuaPlatformMacros(mod, target);

    return b.addLibrary(.{
        .name = "lua-repl",
        .linkage = .static,
        .root_module = mod,
    });
}

/// Add all the Lua 5.4 core + standard-library C sources directly to
/// `mod`. Compared to building a separate static library and linking,
/// this guarantees the linker doesn't drop "unused" objects — we need
/// every Lua API symbol present in the final binary so C rocks loaded
/// via `dlopen` can resolve them against the host process's symbol
/// table.
fn addLuaSources(
    mod: *std.Build.Module,
    lua_src: *std.Build.Dependency,
    lua_anchor_path: std.Build.LazyPath,
) void {
    const cflags = [_][]const u8{
        "-std=gnu99",
        "-Wall",
        "-Wextra",
        "-Wno-unused-parameter",
    };
    mod.addCSourceFiles(.{
        .root = lua_src.path("src"),
        .files = &lua_files,
        .flags = &cflags,
    });
    // Tiny extra TU (codegen'd at build time): takes the address of
    // every Lua API function into a `__attribute__((used))` array.
    // This forces the linker to keep every API function in the binary
    // even under ReleaseFast's LTO and gc-sections, regardless of
    // whether our own code references them. C rocks loaded via
    // `dlopen` (luv.so etc.) need every public Lua symbol resolvable
    // in the host process's symbol table; combined with
    // `rdynamic = true` on the executable, this gets them all into
    // the dynamic symbol table.
    mod.addCSourceFile(.{
        .file = lua_anchor_path,
        .flags = &cflags,
    });
    addLuaPlatformMacros(mod, mod.resolved_target.?);
}

fn addLuaPlatformMacros(
    mod: *std.Build.Module,
    target: std.Build.ResolvedTarget,
) void {
    // Tell Lua which platform features are available. The macros change
    // which `dlopen`/readline/etc. paths Lua compiles in.
    switch (target.result.os.tag) {
        .macos => mod.addCMacro("LUA_USE_MACOSX", ""),
        .linux => mod.addCMacro("LUA_USE_LINUX", ""),
        .freebsd, .netbsd, .openbsd => mod.addCMacro("LUA_USE_POSIX", ""),
        else => {},
    }
}

/// Codegen step: walk the luarocks tarball, emit a Zig module that
/// exposes every Lua source as a `@embedFile`d entry plus a top-level
/// table mapping `require` paths (e.g. `"luarocks.core.cfg"`) to those
/// contents. The runtime installs this table into `package.preload` so
/// `require("luarocks.*")` resolves without touching disk.
///
/// The generator emits `@embedFile("luarocks/<...>.lua")`-style paths.
/// We then materialize the luarocks source tree alongside the
/// generated Zig file via `addCopyDirectory`, so the embedded paths
/// resolve against the same root the module compiles from. (`@embedFile`
/// only allows reading files inside the module's import-path tree.)
///
/// Two outputs are present in the resulting module:
///   - `pub const files: []const Entry` — { require_name, contents }
///   - `pub const luarocks_main` / `pub const luarocks_admin_main`
///     for the two `src/bin/` driver scripts.
fn generateLuaAnchor(
    b: *std.Build,
    lua_src: *std.Build.Dependency,
) std.Build.LazyPath {
    const tool = b.addExecutable(.{
        .name = "gen-lua-anchor",
        .root_module = b.createModule(.{
            .root_source_file = b.path("build/gen_lua_anchor.zig"),
            .target = b.graph.host,
            .optimize = .Debug,
        }),
    });

    const run = b.addRunArtifact(tool);
    run.addDirectoryArg(lua_src.path("src"));
    return run.addOutputFileArg("lua_anchor.c");
}

fn generateLuarocksEmbed(
    b: *std.Build,
    luarocks_src: *std.Build.Dependency,
) std.Build.LazyPath {
    const tool = b.addExecutable(.{
        .name = "gen-luarocks-embed",
        .root_module = b.createModule(.{
            .root_source_file = b.path("build/gen_luarocks_embed.zig"),
            .target = b.graph.host,
            .optimize = .Debug,
        }),
    });

    const run = b.addRunArtifact(tool);
    // Pass a marker arg the tool will treat as the "embed-relative"
    // subpath — every `@embedFile` reference uses this prefix so
    // they resolve against the same directory the generated zig file
    // lives in (the one we set up next via addWriteFiles).
    run.addArg("luarocks_src");
    run.addDirectoryArg(luarocks_src.path("src"));
    const gen_file = run.addOutputFileArg("embedded_luarocks.zig");

    // Stage the generated zig file next to a copy of the luarocks src
    // tree, so `@embedFile("luarocks_src/...")` resolves.
    const wf = b.addWriteFiles();
    const out_zig = wf.addCopyFile(gen_file, "embedded_luarocks.zig");
    _ = wf.addCopyDirectory(luarocks_src.path("src"), "luarocks_src", .{});
    return out_zig;
}

/// Codegen step: walk the in-repo `agent/` tree and emit a Zig module
/// embedding every file. Bootstrap stages the result under
/// `<data home>/agent/` on first run, where the runtime's extension
/// loader finds it as the "base" layer (below user and project).
///
/// Unlike `generateLuarocksEmbed`, the agent tree lives in-repo and
/// its contents change as we add/edit tools. `addDirectoryArg` on a
/// local source dir does NOT hash directory contents into the cache
/// key (only the path string), so editing a file under `agent/`
/// wouldn't invalidate this step's cache. To make cache invalidation
/// correct, we enumerate the tree at *build-script execution time*
/// and call `addFileInput` for every file we find. Each file then
/// participates in the cache key.
///
/// `addCopyDirectory` (below) still does the actual staging of the
/// tree alongside the generated zig file so `@embedFile("agent_src/...")`
/// references resolve.
fn generateAgentEmbed(b: *std.Build) std.Build.LazyPath {
    const tool = b.addExecutable(.{
        .name = "gen-agent-embed",
        .root_module = b.createModule(.{
            .root_source_file = b.path("build/gen_agent_embed.zig"),
            .target = b.graph.host,
            .optimize = .Debug,
        }),
    });

    const run = b.addRunArtifact(tool);
    // Marker subpath: each emitted `@embedFile` reference is
    // `agent_src/<rel>`, and we stage the tree under that name.
    run.addArg("agent_src");
    run.addDirectoryArg(b.path("agent"));
    const gen_file = run.addOutputFileArg("embedded_agent.zig");

    // Enumerate every file under `agent/` and register it as an
    // explicit cache input. This is what makes `zig build` notice
    // edits to e.g. `agent/tools/read.lua` without a manual
    // `rm -rf .zig-cache`.
    addAgentTreeFileInputs(b, run, "agent") catch |err| {
        std.debug.panic("failed to enumerate agent/ tree: {t}", .{err});
    };

    const wf = b.addWriteFiles();
    const out_zig = wf.addCopyFile(gen_file, "embedded_agent.zig");
    _ = wf.addCopyDirectory(b.path("agent"), "agent_src", .{});
    return out_zig;
}

/// Recursively walk `subpath` under the build root and call
/// `addFileInput` on every regular file. Used to give the agent-embed
/// codegen accurate cache invalidation. Dotfiles (any path segment
/// starting with `.`) are skipped to match the codegen's filter.
fn addAgentTreeFileInputs(
    b: *std.Build,
    run: *std.Build.Step.Run,
    subpath: []const u8,
) !void {
    const io = b.graph.io;
    var dir = b.build_root.handle.openDir(io, subpath, .{ .iterate = true }) catch |err| switch (err) {
        error.FileNotFound => return,
        else => return err,
    };
    defer dir.close(io);

    var walker = try dir.walk(b.allocator);
    defer walker.deinit();

    while (try walker.next(io)) |entry| {
        if (entry.kind != .file) continue;
        if (entry.basename.len == 0 or entry.basename[0] == '.') continue;
        if (std.mem.indexOf(u8, entry.path, "/.") != null) continue;
        const rel = b.pathJoin(&.{ subpath, entry.path });
        run.addFileInput(b.path(rel));
    }
}

/// Codegen step: emit a Zig module that exposes every Lua public header
/// from the Lua source tarball as embedded bytes. The bootstrap stages
/// these under `<data home>/rocks/lua-X.Y.Z/include/` so luarocks can
/// compile C rocks against them.
fn generateLuaHeadersEmbed(
    b: *std.Build,
    lua_src: *std.Build.Dependency,
) std.Build.LazyPath {
    const tool = b.addExecutable(.{
        .name = "gen-lua-headers-embed",
        .root_module = b.createModule(.{
            .root_source_file = b.path("build/gen_lua_headers_embed.zig"),
            .target = b.graph.host,
            .optimize = .Debug,
        }),
    });

    const run = b.addRunArtifact(tool);
    // Marker subpath: each emitted `@embedFile` reference is
    // `lua_src/<header>`, and we stage the headers under that name.
    run.addArg("lua_src");
    run.addDirectoryArg(lua_src.path("src"));
    const gen_file = run.addOutputFileArg("embedded_lua_headers.zig");

    const wf = b.addWriteFiles();
    const out_zig = wf.addCopyFile(gen_file, "embedded_lua_headers.zig");
    _ = wf.addCopyDirectory(lua_src.path("src"), "lua_src", .{});
    return out_zig;
}

/// Codegen step: embed the compiled `libpanto-lua` `panto.so` into a Zig
/// module the bootstrap stages onto the embedded VM's `package.cpath`.
///
/// We address the artifact via `dep.artifact("panto")` (the `addLibrary`
/// Compile step named `panto` in `libpanto-lua/build.zig`) and embed its
/// emitted binary by bytes — name-agnostic, so the upstream `libpanto.so`/
/// `libpanto.dylib` filename is irrelevant; we always stage it as
/// `panto.so`. The `.so` is copied next to the generated module so
/// `@embedFile` can resolve it.
fn generatePantoSoEmbed(
    b: *std.Build,
    panto_lua_dep: *std.Build.Dependency,
) std.Build.LazyPath {
    const so_path = panto_lua_dep.artifact("panto").getEmittedBin();

    const tool = b.addExecutable(.{
        .name = "gen-panto-so-embed",
        .root_module = b.createModule(.{
            .root_source_file = b.path("build/gen_panto_so_embed.zig"),
            .target = b.graph.host,
            .optimize = .Debug,
        }),
    });

    const run = b.addRunArtifact(tool);
    // The generated module `@embedFile`s exactly this name.
    run.addArg("panto.so");
    const gen_file = run.addOutputFileArg("embedded_panto_so.zig");

    const wf = b.addWriteFiles();
    const out_zig = wf.addCopyFile(gen_file, "embedded_panto_so.zig");
    _ = wf.addCopyFile(so_path, "panto.so");
    return out_zig;
}

// Lua 5.4.x core VM + standard library. Excludes lua.c (interpreter entry
// point) and luac.c (compiler entry point).
const lua_files = [_][]const u8{
    // Core VM
    "lapi.c",     "lcode.c",    "lctype.c",   "ldebug.c",  "ldo.c",
    "ldump.c",    "lfunc.c",    "lgc.c",      "llex.c",    "lmem.c",
    "lobject.c",  "lopcodes.c", "lparser.c",  "lstate.c",  "lstring.c",
    "ltable.c",   "ltm.c",      "lundump.c",  "lvm.c",     "lzio.c",
    // Auxiliary + standard library
    "lauxlib.c",  "lbaselib.c", "lcorolib.c", "ldblib.c",  "liolib.c",
    "lmathlib.c", "loadlib.c",  "loslib.c",   "lstrlib.c", "ltablib.c",
    "lutf8lib.c", "linit.c",
};