const std = @import("std");
const builtin = @import("builtin");
const assert = std.debug.assert;
const Allocator = std.mem.Allocator;
const build_config = @import("../build_config.zig");

/// A diagnostic message from parsing. This is used to provide additional
/// human-friendly warnings and errors about the parsed data.
///
/// All of the memory for the diagnostic is allocated from the arena
/// associated with the config structure. If an arena isn't available
/// then diagnostics are not supported.
pub const Diagnostic = struct {
    location: Location = .none,
    key: [:0]const u8 = "",
    message: [:0]const u8,

    /// Write the full user-friendly diagnostic message to the writer.
    pub fn write(self: *const Diagnostic, writer: anytype) !void {
        switch (self.location) {
            .none => {},
            .cli => |index| try writer.print("cli:{}:", .{index}),
            .file => |file| try writer.print(
                "{s}:{}:",
                .{ file.path, file.line },
            ),
        }

        if (self.key.len > 0) {
            try writer.print("{s}: ", .{self.key});
        } else if (self.location != .none) {
            try writer.print(" ", .{});
        }

        try writer.print("{s}", .{self.message});
    }
};

/// The possible locations for a diagnostic message. This is used
/// to provide context for the message.
pub const Location = union(enum) {
    none,
    cli: usize,
    file: struct {
        path: []const u8,
        line: usize,
    },

    pub const Key = @typeInfo(Location).Union.tag_type.?;

    pub fn fromIter(iter: anytype) Location {
        const Iter = t: {
            const T = @TypeOf(iter);
            break :t switch (@typeInfo(T)) {
                .Pointer => |v| v.child,
                .Struct => T,
                else => return .none,
            };
        };

        if (!@hasDecl(Iter, "location")) return .none;
        return iter.location() orelse .none;
    }
};

/// A list of diagnostics. The "_diagnostics" field must be this type
/// for diagnostics to be supported. If this field is an incorrect type
/// a compile-time error will be raised.
///
/// This is implemented as a simple wrapper around an array list
/// so that we can inject some logic around adding diagnostics
/// and potentially in the future structure them differently.
pub const DiagnosticList = struct {
    /// The list of diagnostics.
    list: std.ArrayListUnmanaged(Diagnostic) = .{},

    /// Precomputed data for diagnostics. This is used specifically
    /// when we build libghostty so that we can precompute the messages
    /// and return them via the C API without allocating memory at
    /// call time.
    precompute: Precompute = precompute_init,

    const precompute_enabled = switch (build_config.artifact) {
        // We enable precompute for tests so that the logic is
        // semantically analyzed and run.
        .exe, .wasm_module => builtin.is_test,

        // We specifically want precompute for libghostty.
        .lib => true,
    };
    const Precompute = if (precompute_enabled) struct {
        messages: std.ArrayListUnmanaged([:0]const u8) = .{},
    } else void;
    const precompute_init: Precompute = if (precompute_enabled) .{} else {};

    pub fn append(
        self: *DiagnosticList,
        alloc: Allocator,
        diag: Diagnostic,
    ) Allocator.Error!void {
        try self.list.append(alloc, diag);
        errdefer _ = self.list.pop();

        if (comptime precompute_enabled) {
            var buf = std.ArrayList(u8).init(alloc);
            defer buf.deinit();
            try diag.write(buf.writer());

            const owned: [:0]const u8 = try buf.toOwnedSliceSentinel(0);
            errdefer alloc.free(owned);

            try self.precompute.messages.append(alloc, owned);
            errdefer _ = self.precompute.messages.pop();

            assert(self.precompute.messages.items.len == self.list.items.len);
        }
    }

    pub fn empty(self: *const DiagnosticList) bool {
        return self.list.items.len == 0;
    }

    pub fn items(self: *const DiagnosticList) []const Diagnostic {
        return self.list.items;
    }

    /// Returns true if there are any diagnostics for the given
    /// location type.
    pub fn containsLocation(
        self: *const DiagnosticList,
        location: Location.Key,
    ) bool {
        for (self.list.items) |diag| {
            if (diag.location == location) return true;
        }

        return false;
    }
};