/**
 * Structured prompt contract output from the context compiler.
 *
 * A PromptContract is the final, budget-aware assembly of prompt sections
 * ready to be rendered into a prompt string.  It carries full traceability
 * back to its data sources via traceId links on each section.
 */

import type { KernelSnapshot } from "../kernel/snapshots.ts";
import type { GateResult, KdFact, KdToolResultContract, KdWorkingSet } from "../types.ts";
import type { EvidenceSummary } from "../kernel/snapshots.ts";

// ── Section source taxonomy ──────────────────────────────────────────

/**
 * Every prompt section must declare which data source produced its content.
 * This enables downstream consumers to trace each section back to its origin.
 */
export type PromptSectionSource =
	| "kernel-snapshot"
	| "run-state"
	| "facts"
	| "evidence"
	| "gate-decision"
	| "tool-result"
	| "ledger"
	| "project-context"
	| "policy-summary"
	| "control-frame"
	| "working-set"
	| "user-input";

// ── PromptSection ────────────────────────────────────────────────────

/**
 * A single section within the prompt contract.
 *
 * Each section carries:
 * - content produced by a specific data source
 * - a priority used for trim ordering (lower = higher priority, trimmed last)
 * - an optional character budget; when exceeded the content is truncated
 * - an `always` flag marking uncuttable sections (control-frame, user-input, etc.)
 * - a traceId linking back to the originating data record or snapshot
 */
export interface PromptSection {
	/** Stable identifier for this section (e.g. "status", "control"). */
	id: string;
	/** Human-readable section heading. */
	title: string;
	/** Section body content. */
	content: string;
	/** Data source taxonomy. */
	source: PromptSectionSource;
	/** Trim priority — lower values survive budget trimming first (default: 100). */
	priority: number;
	/** Per-section character budget (optional override).  When set, content exceeding this limit is truncated independently of the global budget. */
	budget?: number;
	/** When true, this section is never trimmed regardless of budget pressure. */
	always: boolean;
	/** Whether this section should be included in the final contract.  When false, the section is excluded entirely. */
	include: boolean;
	/** Traceability link to the originating data record (run.id, fact.key, evidence entry id, etc.). */
	traceId: string;
}

// ── TrimLogEntry ─────────────────────────────────────────────────────

/**
 * Records a single trim action applied to a section during budget enforcement.
 */
export interface TrimLogEntry {
	/** The section id that was trimmed. */
	sectionId: string;
	/** Character count before trimming. */
	originalChars: number;
	/** Character count after trimming. */
	trimmedChars: number;
	/** Reason for the trim action. */
	reason: "per-section-budget" | "global-budget" | "excluded";
}

// ── PromptContract ───────────────────────────────────────────────────

/**
 * Final, budget-aware assembly of prompt sections.
 *
 * Produced by `PromptSectionRegistry.compile()`.  Carries aggregate budget
 * metrics and a full trim log for audit purposes.
 */
export interface PromptContract {
	/** Ordered list of sections included in this contract. */
	sections: PromptSection[];
	/** Total character count across all included sections. */
	totalChars: number;
	/** Characters consumed after trimming. */
	budgetUsed: number;
	/** Total character budget for this contract. */
	budgetTotal: number;
	/** Log of all trim actions applied during compilation. */
	trimLog: TrimLogEntry[];
	/** Traceability identifier for this contract assembly. */
	traceId: string;
}

// ── CompileContext ────────────────────────────────────────────────────

/**
 * Input data supplied to `PromptSectionRegistry.compile()`.
 *
 * Each field corresponds to a potential prompt section source.
 */
export interface CompileContext {
	/** Current kernel snapshot capturing full run state. */
	kernelSnapshot: KernelSnapshot;
	/** Gate decisions from the current run. */
	gateDecisions: GateResult[];
	/** Current facts from the run. */
	facts: KdFact[];
	/** Aggregated evidence summary. */
	evidenceSummary: EvidenceSummary;
	/** Recent tool results. */
	toolResults: KdToolResultContract[];
	/** Current working set. */
	workingSet?: KdWorkingSet;
	/** User's raw input text for this turn. */
	userInput: string;
	/** Total character budget for the assembled contract. */
	totalBudget: number;
}

// ── PromptContract assembly ──────────────────────────────────────────

/**
 * Assemble a PromptContract from pre-trimmed sections and a budget.
 *
 * This function is called by the registry after all sections are collected
 * and trimmed.  It produces the final contract with aggregate metrics.
 */
export function assembleContract(
	sections: PromptSection[],
	totalBudget: number,
): PromptContract {
	const included = sections.filter((s) => s.include);
	const totalChars = included.reduce((sum, s) => sum + s.content.length, 0);
	const traceId = `contract-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;

	return {
		sections: included,
		totalChars,
		budgetUsed: totalChars,
		budgetTotal: totalBudget,
		trimLog: [],
		traceId,
	};
}

/**
 * Apply per-section budget limits, then global budget pressure.
 *
 * Sections marked `always: true` are never trimmed.
 * Remaining sections are trimmed lowest-priority-first until the total
 * character count fits within `totalBudget`.
 */
export function enforceBudgets(
	sections: PromptSection[],
	totalBudget: number,
): { sections: PromptSection[]; trimLog: TrimLogEntry[] } {
	const trimLog: TrimLogEntry[] = [];

	// Phase 1: Apply per-section budgets to individual sections.
	let current = sections.map((section) => {
		if (!section.include) {
			trimLog.push({
				sectionId: section.id,
				originalChars: section.content.length,
				trimmedChars: 0,
				reason: "excluded",
			});
			return section;
		}

		if (section.budget != null && section.content.length > section.budget) {
			const trimmed = applyPerSectionBudget(section.content, section.budget);
			trimLog.push({
				sectionId: section.id,
				originalChars: section.content.length,
				trimmedChars: trimmed.length,
				reason: "per-section-budget",
			});
			return { ...section, content: trimmed };
		}

		return section;
	});

	// Phase 2: Enforce global budget — trim by priority (highest number first).
	const totalChars = current.filter((s) => s.include).reduce((sum, s) => sum + s.content.length, 0);

	if (totalChars > totalBudget) {
		const sorted = [...current]
			.filter((s) => s.include && !s.always)
			.sort((a, b) => b.priority - a.priority); // highest priority number = trimmed first

		let overBudget = totalChars - totalBudget;

		for (const section of sorted) {
			if (overBudget <= 0) break;

			const idx = current.findIndex((s) => s.id === section.id);
			if (idx < 0) continue;

			const original = current[idx].content;
			const canCut = original.length - 100; // leave at least 100 chars
			if (canCut <= 0) continue;

			const cut = Math.min(canCut, overBudget);
			const trimmed = original.slice(0, original.length - cut) + "\n\n[...已截断；超出预算...]";

			trimLog.push({
				sectionId: section.id,
				originalChars: original.length,
				trimmedChars: trimmed.length,
				reason: "global-budget",
			});

			current[idx] = { ...current[idx], content: trimmed };
			overBudget -= cut;
		}
	}

	return { sections: current, trimLog };
}

/**
 * Apply a per-section character budget by truncating content.
 * Preserves a truncation marker so consumers know content was cut.
 */
function applyPerSectionBudget(content: string, budget: number): string {
	if (content.length <= budget) return content;
	return `${content.slice(0, budget)}\n\n[...已截断；完整内容读取本地文件...]`;
}