//! Loader for `~/.config/panto/models.toml`.
//!
//! Schema:
//!
//!     [<provider>.<model>]
//!     input       = <float>   # USD per million tokens (fresh input)
//!     output      = <float>   # USD per million tokens
//!     cache_read  = <float>   # USD per million tokens (optional; default "unknown")
//!     cache_write = <float>   # USD per million tokens (optional; default "unknown")
//!
//! All four price fields are optional at the parse layer. Any field
//! omitted from the TOML comes through as `null` in the in-memory
//! `Pricing`, which means "unknown price for this token category" —
//! NOT "zero." If the model later reports usage in an unknown
//! category (e.g. gpt-4o reads from prompt cache but the TOML omitted
//! `cache_read`), session cost degenerates to "unknown" rather than
//! silently treating that usage as free. To declare a category as a
//! known zero (e.g. OpenAI doesn't bill a cache-write rate), write
//! `cache_write = 0` explicitly.
//!
//! `<provider>` is `openai` or `anthropic` (matching pantograph's API
//! styles). `<model>` is the model id pantograph sends to the API. Both
//! are TOML "dotted-key" path segments; quote them if they contain
//! characters TOML doesn't allow bare (`-`, `.`, `:` etc. — `-` is OK
//! bare; `.` requires quoting since dots separate path segments).
//!
//! Example:
//!
//!     [anthropic."claude-sonnet-4-20250514"]
//!     input       = 3.0
//!     output      = 15.0
//!     cache_read  = 0.3
//!     cache_write = 3.75
//!
//!     [openai.gpt-4o]
//!     input  = 2.5
//!     output = 10.0
//!
//! The model id in the section header may also be unquoted when it
//! contains no `.` or other reserved chars (e.g. `gpt-4o`); pantograph
//! reads either form. We do not currently bake in default pricing —
//! a missing entry (or a present entry with missing fields) surfaces
//! as "unknown cost" and the display layer formats accordingly.

const std = @import("std");
const Allocator = std.mem.Allocator;
const Io = std.Io;

const toml = @import("toml");
const panto = @import("panto");

pub const Pricing = panto.pricing.Pricing;
pub const Registry = panto.pricing.Registry;

/// Resolve the absolute path to `models.toml`. Honors `XDG_CONFIG_HOME`,
/// falling back to `$HOME/.config`. Caller owns the returned slice.
pub fn configPath(allocator: Allocator, environ_map: *const std.process.Environ.Map) ![]u8 {
    if (environ_map.get("XDG_CONFIG_HOME")) |xdg| {
        return try std.fs.path.join(allocator, &.{ xdg, "panto", "models.toml" });
    }
    if (environ_map.get("HOME")) |home| {
        return try std.fs.path.join(allocator, &.{ home, ".config", "panto", "models.toml" });
    }
    return error.NoHomeDirectory;
}

/// Load `models.toml` into a fresh `Registry`. If the file does not
/// exist, returns an empty registry (no error — missing config is fine).
///
/// On parse errors, returns `error.InvalidModelsToml` after logging the
/// line/column of the first error.
pub fn loadFromPath(
    allocator: Allocator,
    io: Io,
    path: []const u8,
) !Registry {
    var reg = Registry.init(allocator);
    errdefer reg.deinit();

    const file = Io.Dir.cwd().openFile(io, path, .{ .mode = .read_only }) catch |err| switch (err) {
        error.FileNotFound => return reg, // empty registry; perfectly fine.
        else => return err,
    };
    defer file.close(io);

    const file_len = try file.length(io);
    const bytes = try allocator.alloc(u8, @intCast(file_len));
    defer allocator.free(bytes);
    _ = try file.readPositionalAll(io, bytes, 0);

    try parseInto(&reg, bytes);
    return reg;
}

/// Parse a TOML string into the given registry. Useful for tests.
pub fn parseInto(reg: *Registry, source: []const u8) !void {
    const alloc = reg.allocator;
    const result = toml.parseWithError(alloc, source, .{});
    switch (result) {
        .err => |e| {
            // Silenced in tests so the test runner doesn't flag the
            // expected-failure case as a real error.
            if (!@import("builtin").is_test) {
                std.log.err(
                    "models.toml: parse error at line {d}, column {d}: {s}",
                    .{ e.line, e.column, e.message },
                );
            }
            return error.InvalidModelsToml;
        },
        .ok => |doc| {
            defer {
                var d = doc;
                d.deinit();
            }
            try ingestDocument(reg, doc);
        },
    }
}

fn ingestDocument(reg: *Registry, doc: *toml.Document) !void {
    // Root is a table of provider -> table of model -> { input, output, ... }.
    const root_val: *const toml.Value = doc.root;
    if (root_val.* != .table) return;
    var provider_it = toml.tableIterator(root_val);
    while (provider_it.next()) |provider_entry| {
        const provider = provider_entry.key;
        const provider_val: *const toml.Value = provider_entry.value;
        if (provider_val.* != .table) continue;
        var model_it = toml.tableIterator(provider_val);
        while (model_it.next()) |model_entry| {
            const model = model_entry.key;
            const v: *const toml.Value = model_entry.value;
            if (v.* != .table) continue;
            const pricing = pricingFromValue(v);
            try reg.set(provider, model, pricing);
        }
    }
}

fn pricingFromValue(v: *const toml.Value) Pricing {
    return .{
        .input = readPriceField(v, "input"),
        .output = readPriceField(v, "output"),
        .cache_read = readPriceField(v, "cache_read"),
        .cache_write = readPriceField(v, "cache_write"),
    };
}

/// Returns `null` if the field is absent or has a type we can't
/// interpret as a price. An explicit `0` (or `0.0`) comes through as a
/// known zero, not `null` — callers rely on that distinction.
fn readPriceField(table: *const toml.Value, name: []const u8) ?u64 {
    const field = table.get(name) orelse return null;
    // Accept either floats (the natural form) or integers (the user
    // wrote `3` instead of `3.0`).
    if (field.asF64()) |f| return Pricing.fromDollarsPerMtok(f);
    if (field.asI64()) |i| return Pricing.fromDollarsPerMtok(@floatFromInt(i));
    return null;
}

// =============================================================================
// Tests
// =============================================================================

const testing = std.testing;

test "parseInto: two providers, multiple models" {
    var reg = Registry.init(testing.allocator);
    defer reg.deinit();

    const src =
        \\[anthropic."claude-sonnet-4-20250514"]
        \\input = 3.0
        \\output = 15.0
        \\cache_read = 0.3
        \\cache_write = 3.75
        \\
        \\[openai.gpt-4o]
        \\input = 2.5
        \\output = 10.0
        \\cache_read = 1.25
        \\
        \\[openai.gpt-4o-mini]
        \\input = 0.15
        \\output = 0.6
    ;
    try parseInto(&reg, src);

    const anth = reg.get("anthropic", "claude-sonnet-4-20250514").?;
    try testing.expectEqual(@as(?u64, 300), anth.input);
    try testing.expectEqual(@as(?u64, 1500), anth.output);
    try testing.expectEqual(@as(?u64, 30), anth.cache_read);
    try testing.expectEqual(@as(?u64, 375), anth.cache_write);

    const oa = reg.get("openai", "gpt-4o").?;
    try testing.expectEqual(@as(?u64, 250), oa.input);
    try testing.expectEqual(@as(?u64, 1000), oa.output);
    try testing.expectEqual(@as(?u64, 125), oa.cache_read);
    // cache_write absent in source — stays unknown, NOT silently 0.
    try testing.expectEqual(@as(?u64, null), oa.cache_write);

    const mini = reg.get("openai", "gpt-4o-mini").?;
    try testing.expectEqual(@as(?u64, 15), mini.input);
    try testing.expectEqual(@as(?u64, 60), mini.output);
    try testing.expectEqual(@as(?u64, null), mini.cache_read);
    try testing.expectEqual(@as(?u64, null), mini.cache_write);
}

test "parseInto: integer values are accepted (user writes `3` not `3.0`)" {
    var reg = Registry.init(testing.allocator);
    defer reg.deinit();

    const src =
        \\[openai.gpt-4o]
        \\input = 3
        \\output = 15
    ;
    try parseInto(&reg, src);
    const p = reg.get("openai", "gpt-4o").?;
    try testing.expectEqual(@as(?u64, 300), p.input);
    try testing.expectEqual(@as(?u64, 1500), p.output);
}

test "parseInto: missing optional fields stay null (unknown, not zero)" {
    var reg = Registry.init(testing.allocator);
    defer reg.deinit();

    const src =
        \\[openai.gpt-4o]
        \\input = 2.5
        \\output = 10.0
    ;
    try parseInto(&reg, src);
    const p = reg.get("openai", "gpt-4o").?;
    try testing.expectEqual(@as(?u64, null), p.cache_read);
    try testing.expectEqual(@as(?u64, null), p.cache_write);
}

test "parseInto: explicit 0 is a known zero, distinct from omission" {
    // OpenAI doesn't charge for cache writes. Writing `cache_write = 0`
    // in the TOML must produce a known 0 — not null — so cost stays
    // computable on turns that report cache_write usage.
    var reg = Registry.init(testing.allocator);
    defer reg.deinit();

    const src =
        \\[openai.gpt-4o]
        \\input = 2.5
        \\output = 10.0
        \\cache_read = 1.25
        \\cache_write = 0
    ;
    try parseInto(&reg, src);
    const p = reg.get("openai", "gpt-4o").?;
    try testing.expectEqual(@as(?u64, 0), p.cache_write);
}

test "parseInto: malformed TOML returns InvalidModelsToml" {
    var reg = Registry.init(testing.allocator);
    defer reg.deinit();
    try testing.expectError(error.InvalidModelsToml, parseInto(&reg, "this is not valid toml = ="));
}

test "loadFromPath: missing file returns empty registry, no error" {
    const io = testing.io;
    var reg = try loadFromPath(testing.allocator, io, "/nonexistent/path/models.toml");
    defer reg.deinit();
    try testing.expectEqual(@as(usize, 0), reg.count());
}

test "configPath: XDG_CONFIG_HOME wins" {
    const a = testing.allocator;
    var env: std.process.Environ.Map = .init(a);
    defer env.deinit();
    try env.put("XDG_CONFIG_HOME", "/custom/cfg");
    try env.put("HOME", "/ignored");
    const got = try configPath(a, &env);
    defer a.free(got);
    try testing.expectEqualStrings("/custom/cfg/panto/models.toml", got);
}

test "configPath: falls back to HOME/.config" {
    const a = testing.allocator;
    var env: std.process.Environ.Map = .init(a);
    defer env.deinit();
    try env.put("HOME", "/home/user");
    const got = try configPath(a, &env);
    defer a.free(got);
    try testing.expectEqualStrings("/home/user/.config/panto/models.toml", got);
}