// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package oracle

import (
	"fmt"
	"go/token"

	"golang.org/x/tools/go/callgraph"
	"golang.org/x/tools/go/loader"
	"golang.org/x/tools/go/ssa"
	"golang.org/x/tools/go/ssa/ssautil"
	"golang.org/x/tools/oracle/serial"
)

// Callers reports the possible callers of the function
// immediately enclosing the specified source location.
//
func callers(q *Query) error {
	lconf := loader.Config{Build: q.Build}

	if err := setPTAScope(&lconf, q.Scope); err != nil {
		return err
	}

	// Load/parse/type-check the program.
	lprog, err := lconf.Load()
	if err != nil {
		return err
	}
	q.Fset = lprog.Fset

	qpos, err := parseQueryPos(lprog, q.Pos, false)
	if err != nil {
		return err
	}

	prog := ssautil.CreateProgram(lprog, 0)

	ptaConfig, err := setupPTA(prog, lprog, q.PTALog, q.Reflection)
	if err != nil {
		return err
	}

	pkg := prog.Package(qpos.info.Pkg)
	if pkg == nil {
		return fmt.Errorf("no SSA package")
	}
	if !ssa.HasEnclosingFunction(pkg, qpos.path) {
		return fmt.Errorf("this position is not inside a function")
	}

	// Defer SSA construction till after errors are reported.
	prog.Build()

	target := ssa.EnclosingFunction(pkg, qpos.path)
	if target == nil {
		return fmt.Errorf("no SSA function built for this location (dead code?)")
	}

	// TODO(adonovan): opt: if function is never address-taken, skip
	// the pointer analysis.  Just look for direct calls.  This can
	// be done in a single pass over the SSA.

	// Run the pointer analysis, recording each
	// call found to originate from target.
	ptaConfig.BuildCallGraph = true
	cg := ptrAnalysis(ptaConfig).CallGraph
	cg.DeleteSyntheticNodes()
	edges := cg.CreateNode(target).In
	// TODO(adonovan): sort + dedup calls to ensure test determinism.

	q.result = &callersResult{
		target:    target,
		callgraph: cg,
		edges:     edges,
	}
	return nil
}

type callersResult struct {
	target    *ssa.Function
	callgraph *callgraph.Graph
	edges     []*callgraph.Edge
}

func (r *callersResult) display(printf printfFunc) {
	root := r.callgraph.Root
	if r.edges == nil {
		printf(r.target, "%s is not reachable in this program.", r.target)
	} else {
		printf(r.target, "%s is called from these %d sites:", r.target, len(r.edges))
		for _, edge := range r.edges {
			if edge.Caller == root {
				printf(r.target, "the root of the call graph")
			} else {
				printf(edge, "\t%s from %s", edge.Description(), edge.Caller.Func)
			}
		}
	}
}

func (r *callersResult) toSerial(res *serial.Result, fset *token.FileSet) {
	var callers []serial.Caller
	for _, edge := range r.edges {
		callers = append(callers, serial.Caller{
			Caller: edge.Caller.Func.String(),
			Pos:    fset.Position(edge.Pos()).String(),
			Desc:   edge.Description(),
		})
	}
	res.Callers = callers
}